Two gardening related tips.
If you hover over a plant, it tells you what it is. But if you can get your cursor just right, hovering over the fruit/flower it will tell you what it is worth. I think we all know to let them wait and not pounce the moment they become harvestable. If you leave the lot (or go into CAS) and come back, in evolved plants (not sure about basic plants) when you come back from the loading screen, they will be worth more. You can do this multiple times.
If you have a perfect plant and you graft onto it, the grafted plant becomes perfect. You don't have to spend all you time evolving. The best application would be to get a plant that you can evolve up to perfect quickly, then graft the slowpokes onto it. Onnce you get the harvest, plant those and you are on your way to making big money.
Oh, and a bonus tip: A cowplant berry is worth 20. Plant that baby and immediately it is worth 475. You don't have to wait for it to grow.